This invention relates in general to the field of pipe line gaskets, and more particularly to a dielectric gasket for preventing galvanic corrosion of pipe lines.
Pipe lines are used throughout the world to transport many different materials over long and short distances and over some of the most remote and populated areas of the world. Some of the most common materials transported are oil, gas, and water. For example, the $8 billion dollar Trans Alaska Pipeline transports crude oil across more than 800 miles of environmentally sensitive and remote land. Typically, a pipe line is constructed by welding individual joints of pipe into long sections. Pipe lines also incorporate pipe flanges to join sections together for various reasons. A gasket is typically used to form a seal between mating pipe flanges.
A leak in a pipe line can be extremely expensive. In order to repair the leak, the pipe line must often be shut down and the material in the pipe line removed before repairs can be made. In many cases, material that leaked from the pipe line must then be cleaned from the surrounding environment. A remote location or treacherous environment can make a leak in a pipe line even more expensive and dangerous to repair.
Many leaks in pipe lines are the result of leakage from a gasket or corrosion of a pipe flange. A gasket must be capable of sealing the joints of a pipe line for an indefinite period in a harsh environment. Since metallic joints of pipe in a pipe line may conduct electricity, the gasket may also be used to prevent external corrosion along buried sections of the pipe line. A dielectric gasket inhibits this form of corrosion by forming an electrical insulating barrier between pipe flanges that prohibits electricity from passing onto the next section of the pipeline.
Previously developed dielectric gaskets have suffered from numerous disadvantages. One disadvantage in prior dielectric gaskets is that dielectric gaskets which incorporate seal grooves in the face of the gasket often form cracks between the seal grooves. Cracks between the seal grooves reduce the strength of the gasket and may propagate through the sealing surfaces of the gasket, resulting in a leak in the dielectric gasket.
A further disadvantage of many dielectric gaskets is that they often necessitate expensive stainless steel metals. Metal is often used to form a metal backbone in a gasket for high pressure applications. In high pressure applications, the metal backbone is typically placed in contact with the material being transported. Expensive stainless steel is often needed for such applications to prevent corrosion of the metal backbone. In addition, in some situations the material being transported will chemically react with and corrode even a stainless steel backbone, causing the gasket to fail.
Some dielectric gaskets are constructed using soft dielectric materials. However, soft dielectric gaskets are easily over-compressed by over-torquing the tie rods. The over-compression forces the soft dielectric material in the gasket to deform and damage the seals or the sealing surfaces of the gasket. Another problem with soft dielectric gaskets is that over-compression can also cause the soft dielectric material to deform in such a manner that the flanges of the pipe contact each other and short-out the dielectric gasket, rendering the dielectric gasket useless.
Other dielectric gaskets are constructed of hard dielectric materials, which require very high tie rod torques in order to form a seal between the two joints of pipe. Although these dielectric gaskets do not readily deform, they are susceptible to cracking under the high loads required to form a seal between the pipe flanges. An additional problem is that these gaskets often do not employ ring type seals in their construction and are therefore vulnerable to wicking. Wicking occurs when the material being transported in the pipe line seeps into the gasket material. Wicking can reduce the material properties of the gasket and can cause a leak in the pipe line or a blow-out of the seal.
Dielectric gaskets are also used to prevent galvanic corrosion between mating flanges of dissimilar metals such as stainless steel and carbon steel. Such flange connections may be used on indoor piping systems such as enclosed process facilities on land or on offshore platforms used to produce oil and gas. In such cases consideration is often given to the possible outbreak of fire and the effect of fire on flange connections. Dielectric gaskets for high pressure with metal backbones conduct heat along the metal backbone directly to the seal grooves. Because of the thermal insulating properties of the dielectric material bonded to the faces of the metal backbone, the heat is confined and intensely directed along the metal backbone. Elastomeric or thermoplastic seals in direct contact with the metal backbone, when exposed to such temperatures, can be damaged or destroyed to the point that they will not function.
Accordingly, a need has arisen for an improved dielectric gasket. The present invention provides a dielectric gasket that substantially eliminates or reduces problems associated with prior dielectric gaskets.
In accordance with one embodiment of the present invention, a dielectric gasket comprises an inner annular disk and an outer annular disk with each disk formed from electrically non-conductive materials. A fluid seal is preferably disposed between the inner annular disk and the outer annular disk.
In another embodiment of the present invention, the dielectric gasket includes a single annular disk formed from at least two distinct rings. In this embodiment, rings are formed in part from two different electrically non-conducting materials, each ring having a first face and a second face. The inner ring is formed from a material resistant to wicking. At least one seal groove is formed within each face of the inner ring of the annular disk with a fluid seal disposed within each seal groove. A pressure communication passage may be formed in the inner ring of the annular disk between corresponding seal grooves located on opposite faces of the annular disk.
In each of the embodiments, a ring stiffener may be disposed within a first face and a second face of the annular disk outboard to the seal(s). The ring stiffeners are physically separated from each other by a portion of the electrically non-conducting material of the outer annular disk in order to insulate the ring stiffeners from each other.
Additionally, in each of the embodiments, a metal backbone or central stiffener may be disposed within the outer annular disk. The present invention maintains a layer of electrically non-conducting material on the inside surface of the outer annular disk and between each pipe flange even when water or other electrically conductive fluids are present.
This invention provides a number of important technical advantages over previous pipeline gaskets, one technical advantage is that the central stiffener and the ring stiffeners provide a backbone to the dielectric gasket that prevents the dielectric gasket from being blown-out under high pressure or high temperature operating conditions. In addition, the central stiffener and ring stiffeners provide structural rigidity to the gasket.
A further technical advantage of the present invention is that the fluid seal prevents wicking from the inner annular seal to the outer annular seal.
A further technical advantage of the present invention is that the electrically non-conducting material will not separate from the metal backbone or stiffener during high pressure operation.
Another technical advantage of the present invention is that the dielectric gasket can withstand mistreatment during installation and continue to operate as intended. Specifically, the present invention will form a desired fluid seal and maintain its integrity as an electrical insulator even when the associated tie rods are improperly torqued. In addition, the present invention does not require high tie rod torques that are often needed when installing a dielectric gasket formed from a hard dielectric material.
Yet another technical advantage of the present invention is that wicking of fluid or material being transported by the pipe line into the gasket material is avoided, thereby reducing the possibility of a blow-out or a fluid leak.
Another technical advantage of the present invention is that damage to the fluid seal from heat due to exposing the external surfaces of the gasket to fire is mitigated.
A further technical advantage of the present invention includes providing a low cost dielectric gasket. In particular, low cost materials may be used in various components of the dielectric gasket to reduce costs and provide a wide spectrum of applications and uses.
Yet another technical advantage of the present invention includes providing a dielectric gasket constructed of individual components which may be mechanically assembled; thereby allowing the seal and other components to be separately manufactured and later assembled into a complete gasket.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.